[vorbis-dev] audio analysis tool?
eds at reric.net
Wed Nov 6 10:01:28 PST 2002
On Wed, Nov 06, 2002 at 02:13:39AM +0100, Segher Boessenkool wrote:
> Eric Seppanen wrote:
> > I'm curious, does anyone know of a way to analyze a wave file to determine
> > the quantity of information in it? For example, given a particular .wav
> > file, how can I find out if it's an original or was encoded to something
> > lossy and back?
> Just look at a spectrogram. Big empty regions at the high frequencies
> ==> lossy. Lots of other features, too (it's not very hard to see which
> codec you're looking at).
That's helpful, but I guess I was imagining that there might be some way
of quantifying how much data is there, for instance having a tool that
could look at an audio input and notice that it never seems to have more
than roughly 128kbps of information in it.
Since vorbis has quality settings, I figured it might be able to quantify
how much signal (not signal magnitude, but quantity of frequency data) is
The other thing that occurs to me is that some codecs may "fake"
high-frequency data when decoding just to fool the uneducated listener.
While a sharp person could probably spot this in a spectrogram, I wonder
if it would be possible for a tool to detect "faked" data and discard it
when measuring the quantity of "useful" data.
I'm wondering how difficult it would be to create such a tool using the
vorbis encoder as a starting point.
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